quantum computer

Quantum Paradox Seen in Diamond.

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A real-life version of Zeno’s ancient Greek conundrum could advance quantum computing

A quantum effect named after an ancient Greek puzzle has been observed in diamond, paving the way for the use of diamond crystals in quantum computer chips.

The quantum Zeno effect gets its name from the Greek philosopher Zeno of Elea, who lived in the fifth century bc and suggested that if the position of a flying arrow is well-defined for a moment of time, then it makes no progress in that moment, and so can never reach its destination.

In the quantum version of the arrow paradox, theoretical physicists posited in 1977 that if a quantum system is measured often enough, its state will be unable to progress, as if it were true that ‘a watched pot never boils’. The hypothesis arises from a fundamental postulate of quantum theory, which says that measuring a property of an object, such as its position, affects its state. The quantum Zeno effect was first observedexperimentally in 1989 in laser-cooled ions trapped by magnetic and electric fields.

Now, quantum physicist Oliver Benson and his colleagues at Humboldt University in Berlin have seen the effect in a diamond crystal — a material that would be easier to manufacture on a large scale for quantum computing. The team posted its paper on the arXiv and it has been accepted for publication in Physical Review A.

Disrupted oscillations
The researchers focused on nitrogen–vacancy (NV) centers, imperfections in diamond that arise where an atom of nitrogen and an empty space replace carbon atoms at two neighboring spots in the crystal lattice. The team used microwaves to change the magnetic spin state of an electron located at an NV center, and then used a laser beam to trigger red fluorescence that revealed which of two possible states the electron was in at any given moment. When they measured the NV center in this way, the researchers found that the oscillation between the two states was disrupted — just as would be expected if the quantum Zeno effect were operating.

“The first step is to see the effect is there, but the next step is to implement quantum gates based on diamond,” says Benson, referring to the quantum analogue of the logic gates that form the integrated circuits in ordinary computer chips. In quantum computing, information is stored in the quantum states of carriers such as photons or diamond defects. But so far, decoherence, a degradation of the delicate states caused by noise in the environment, has prevented researchers from storing more than a few bits of linked quantum information in a diamond crystal at a time. Constantly measuring the states could protect them from uncontrolled decay and allow researchers to scale up the amount of information stored, says Benson.

Ronald Walsworth, an atomic physicist at Harvard University in Cambridge, Massachusetts, whose team made a tentative suggestion in 2010 that the quantum Zeno effect operates in diamond, says that evidence is growing, but that it will probably need to be clearer that the disruption of oscillations is due to the quantum process, and not other effects, before it can be used for quantum computing.

Quantum physicist Ronald Hanson, who works with nitrogen vacancies at Delft University of Technology in the Netherlands, says that Benson’s experiment, together with an April paper showing that spins in NV centers located 3 meters apart can be linked, indicates that diamond is gaining ground as a convenient material for quantum computing. “In a few years, we will be overtaking the ion traps,” he says.

Source: http://www.scientificamerican.com

Quantum boost for artificial intelligence.

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Quantum computers able to learn could attack larger sets of data than classical computers.

Quantum computers of the future will have the potential to give artificial intelligence a major boost, a series of studies suggests.

These computers, which encode information in ‘fuzzy’ quantum states that can be zero and one simultaneously, have the ability to someday solve problems, such as breaking encryption keys, that are beyond the reach of ‘classical’ computers.

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Algorithms developed so far for quantum computers have typically focused on problems such as breaking encryption keys or searching a list — tasks that normally require speed but not a lot of intelligence. But in a series of papers posted online this month on the arXiv preprint server1, 2, 3, Seth Lloyd of the Massachusetts Institute of Technology in Cambridge and his collaborators have put a quantum twist on AI.

The team developed a quantum version of ‘machine learning’, a type of AI in which programs can learn from previous experience to become progressively better at finding patterns in data. Machine learning is popular in applications ranging from e-mail spam filters to online-shopping suggestions. The team’s invention would take advantage of quantum computations to speed up machine-learning tasks exponentially.

At the heart of the scheme is a simpler algorithm that Lloyd and his colleagues developed in 2009 as a way of quickly solving systems of linear equations, each of which is a mathematical statement, such as x + y = 4. Conventional computers produce a solution through tedious number crunching, which becomes prohibitively difficult as the amount of data (and thus the number of equations) grows. A quantum computer can cheat by compressing the information and performing calculations on select features extracted from the data and mapped onto quantum bits, or qubits.

Quantum machine learning takes the results of algebraic manipulations and puts them to good use. Data can be split into groups — a task that is at the core of handwriting- and speech-recognition software — or can be searched for patterns. Massive amounts of information could therefore be manipulated with a relatively small number of qubits.

“We could map the whole Universe — all of the information that has existed since the Big Bang — onto 300 qubits,” Lloyd says.

Such quantum AI techniques could dramatically speed up tasks such as image recognition for comparing photos on the web or for enabling cars to drive themselves — fields in which companies such as Google have invested considerable resources. (One of Lloyd’s collaborators, Masoud Mohseni, is in fact a Google researcher based in Venice, California.)

“It’s really interesting to see that there are new ways to use quantum computers coming up, after focusing mostly on factoring and quantum searches,” says Stefanie Barz at the University of Vienna, who recently demonstrated quantum equation-solving in action. Her team used a simple quantum computer that had two qubits to work out a high-school-level maths problem: a system consisting of two equations4. Another group, led by Jian Pan at the University of Science and Technology of China in Hefei, did the same using four qubits5.

Putting quantum machine learning into practice will be more difficult. Lloyd estimates that a dozen qubits would be needed for a small-scale demonstration.

Source: http://www.nature.com

Step towards quantum computer.

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UNSW researchers have proposed a new way to distinguish between quantum bits that are placed only a few nanometres apart in a silicon chip, taking them a step closer to the construction of a large-scale quantum computer.

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Quantum bits, or qubits, are the basic building blocks of quantum computers – ultra-powerful devices that will offer enormous advantages for solving complex problems.

Professor Michelle Simmons, leader of the research team, said a qubit based on the spin of an individual electron bound to a phosphorus atom within a silicon chip is one of the most promising systems for building a practical quantum computer, due to silicon’s widespread use in the microelectronics industry.

“However, to be able to couple electron-spins on single atom qubits,  the qubits need to be placed with atomic precision, within just a few tens of nanometres of each other,”  she says.

“This poses a technical problem in how to make them, and an operational problem in how to control them independently when they are so close together.”

The UNSW team, in collaboration with theorists at Sandia National Laboratories in New Mexico, has found a solution to both these problems.  Their study is published in the journal Nature Communications.

In a significant feat of atomic engineering, they were able to read-out the spins of individual electrons on a cluster of phosphorus atoms that had been placed precisely in silicon. They also propose a new method for distinguishing between neighbouring qubits that are only a few nanometres apart.

“It is a daunting challenge to rotate the spin of each qubit individually,” says Holger Büch, lead author of the new study.

“But if each electron is hosted by a different number of phosphorus atoms, then the qubits will respond to different electromagnetic fields – and each qubit can be distinguished from the others around it,” he says.

The UNSW team is part of the Australian Centre of Excellence for Quantum Computation and Communication Technology, a world-leading research centre headquartered in Sydney, Australia.

“This is an elegant and satisfying piece of work,” says Professor Simmons, centre director and Mr Büch’s PhD supervisor.

“This first demonstration that we can maintain long spin lifetimes of electrons on multi-donor systems is very powerful. It offers a new method for addressing individual qubits, putting us one step closer to realising a practical, large-scale quantum computer.”

To make the tiny device, the researchers deposited a layer of hydrogen on a silicon wafer and used a scanning tunnelling microscope to create a pattern on the surface in an ultra-high vacuum.

This was then exposed to phosphine gas and annealed at 350 degrees so phosphorus atoms became incorporated precisely into the silicon. The device was then buried in another layer of silicon.

In a quantum computer information is stored in the spin, or magnetic orientation, of an electron. This spin can not only be in the two “classical” states – up and down – but also in a combination of both states at the same time, allowing exponentially larger amounts of information to be stored and processed in parallel.

 

Source: http://sciencealert.com.au

How Does a Quantum Computer Work?

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Watch the video.

URL: http://www.sciencealert.com.au/index.php?option=com_jusertube&view=video&rid=g_IaVepNDT4&yuser=PLI-6-wtgFSgC-nbpwvkTbTICySA2shfkV&auto=1&eh=385&ew=600&st=yes&height=500&width=600

Source: science alert

 

Google Buys a Quantum Computer.

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Google

and a corporation associated with NASA are forming a laboratory to study artificial intelligence by means of computers that use the unusual properties of quantum physics. Their quantum computer, which performs complex calculations thousands of times faster than existing supercomputers, is expected to be in active use in the third quarter of this year.

The Quantum Artificial Intelligence Lab, as the entity is called, will focus on machine learning, which is the way computers take note of patterns of information to improve their outputs. Personalized Internet search and predictions of traffic congestion based on GPS data are examples of machine learning. The field is particularly important for things like facial or voice recognition, biological behavior, or the management of very large and complex systems.

“If we want to create effective environmental policies, we need better models of what’s happening to our climate,” Google said in a blog postannouncing the partnership. “Classical computers aren’t well suited to these types of creative problems.”

Google said it had already devised machine-learning algorithms that work inside the quantum computer, which is made by D-Wave Systems of Burnaby, British Columbia. One could quickly recognize information, saving power on mobile devices, while another was successful at sorting out bad or mislabeled data. The most effective methods for using quantum computation, Google said, involved combining the advanced machines with its clouds of traditional computers.

Google bought the machine in cooperation with the Universities Space Research Association, a nonprofit research corporation that works with NASA and others to advance space science and technology. Outside researchers will be invited to the lab as well.

This year D-Wave sold its first commercial quantum computer to Lockheed Martin. Lockheed officials said the computer would be used for the test and measurement of things like jet aircraft designs, or the reliability of satellite systems.

The D-Wave computer works by framing complex problems in terms of optimal outcomes. The classic example of this type of problem is figuring out the most efficient way a traveling salesman can visit 10 customers, but real-world problems now include hundreds of such variables and contingencies. D-Wave’s machine frames the problem in terms of energy states, and uses quantum physics to rapidly determine an outcome that satisfies the variables with the least use of energy.

In tests last September, an independent researcher found that for some types of problems the quantum computer was 3,600 times faster than traditional supercomputers. According to a D-Wave official, the machine performed even better in Google’s tests, which involved 500 variables with different constraints.

“The tougher, more complex ones had better performance,” said Colin Williams, D-Wave’s director of business development. “For most problems, it was 11,000 times faster, but in the more difficult 50 percent, it was 33,000 times faster. In the top 25 percent, it was 50,000 times faster.” Google declined to comment, aside from the blog post.

The machine Google will use at NASA’s Ames Research facility, located near Google headquarters, makes use of the interactions of 512 quantum bits, or qubits, to determine optimization. They plan to upgrade the machine to 2,048 qubits when this becomes available, probably within the next year or two. That machine could be exponentially more powerful.

Google did not say how it might deploy a quantum computer into its existing global network of computer-intensive data centers, which are among the world’s largest. D-Wave, however, intends eventually for its quantum machine to hook into cloud computing systems, doing the exceptionally hard problems that can then be finished off by regular servers.

Potential applications include finance, health care, and national security, said Vern Brownell, D-Wave’s chief executive. “The long-term vision is the quantum cloud, with a few high-end systems in the back end,” he said. “You could use it to train an algorithm that goes into a phone, or do lots of simulations for a financial institution.”

Mr. Brownell, who founded a computer server company, was also the chief technical officer at Goldman Sachs. Goldman is an investor in D-Wave, with Jeff Bezos, the founder of Amazon.com. Amazon Web Services is another global cloud, which rents data storage, computing, and applications to thousands of companies.

This month D-Wave established an American company, considered necessary for certain types of sales of national security technology to the United States government.

Source: NY times

Quantum computers move a step closer

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Successes at entangling three-circuit systems brighten the prospects for solid-state quantum computing.

Eugenie Samuel Reich

Quantum computing has made another advance along the path from theorists’ darling to working device.

A circuit of four superconducting qubits. Scientists have succeeded in entangling three of these.M. NEELEY

The concept depends on entanglement, a strange phenomenon in which the quantum states of spatially separated systems, called ‘qubits’, become intrinsically linked. The entanglement of two or more qubits sets up a ‘superposition’ of states in which calculations can run in parallel — in principle allowing a quantum computer to race through problems that it would take a classical computer eons to solve.

Such a quantum machine would require hundreds or even thousands of entangled qubits. The maximum reached so far is 12, but some of the systems that researchers are working with, including those depending on the spins of ions, may be hard to scale up. In this issue of Nature, two research groups1 report progress on an alternative approach: entangling qubits made from superconducting circuits, a technology that is amenable to manufacture on electronic chips. “Superconducting qubits are one of the better candidates for building a quantum computer,” says Daniel Gottesman, a quantum researcher at the Perimeter Institute in Waterloo, Canada.

The teams have achieved three-qubit entanglement in such a system, which is significant because three is the minimum number needed for quantum error correction — an essential attribute if quantum computers are ever to become practical. A quantum computer is susceptible to flipping its bits and losing information. Measuring bits to check their values part way through a computation would destroy the superposition. But entangling each bit with two extra bits makes it possible to check two of those bits for errors while allowing the calculation to go forwards in the third.

To construct their qubits, a team led by Rob Schoelkopf of Yale University in New Haven, Connecticut, used superconducting aluminium wires cooled to within a degree of absolute zero. The circuits were linked so that voltage and current oscillations flowing through each one would influence the others, and the entanglement was generated with a sequence of microwave bursts that changed the states of the circuits. The result was a kind of entanglement called a Greenberger–Horne–Zeilinger (GHZ) state, in which the three qubits are in a superposition of all being zero, and all being one.

A second group, led by John Martinis of the University of California, Santa Barbara, also succeeded in creating the GHZ state, as well as a ‘W state’, in which the superposed states feature one qubit with a value of one and the other two with a zero. Neither group has used their three entangled bits to run quantum error correction yet. But Schoelkopf emphasizes that his group has already run another type of algorithm using two-qubit entanglement3. He adds that a future challenge will be finding a way to lengthen the lifetime of the qubits, which lose their information within about 100 operations.

Emanuel Knill, an expert in quantum information science at the National Institute of Standards and Technology in Boulder, Colorado, isn’t sold on the approach, noting that it will be difficult to control multiple qubits from outside a refrigerator. But he says he’s happy to see that both groups prepared their quantum states with decent fidelities, meaning that the states are a good match to those the researchers intended to create. “The challenge,” he says, “is to scale up the number of gates and qubits.”

source:Nature